Lithium-ion secondary batteries and other secondary batteries feature smaller size, lighter weight, higher energy density, and more superior output density than existing batteries. Therefore, such secondary batteries have been favorably used as so-called portable power supplies of personal computers, mobile terminals, and the like and as vehicle driving power supplies.
Examples of modes of such batteries include a sealed nonaqueous electrolyte secondary battery. A sealed nonaqueous electrolyte secondary battery is typically constructed by housing an electrode body constituted by positive and negative electrodes having active material layers that contain active materials in a battery case together with an electrolyte (typically, electrolyte liquid), and mounting a lid body to seal the battery case.
While a sealed nonaqueous electrolyte secondary battery is generally used in a state where voltage is controlled so as to be within a prescribed range (for example, 3.0 V or higher and 4.2 V or lower), overcharge may sometimes occur when a current that is larger than normal is supplied to the battery due to a misoperation or the like and voltage exceeds a prescribed voltage. In consideration thereof, a current interrupt device (CID) is widely used which interrupts a charge current when pressure inside a battery case equals or exceeds prescribed pressure and stops progress of overcharge. Generally, when a battery enters an overcharged state, an electrolyte (typically, a nonaqueous solvent) or the like is electrolyzed and gas is generated. The current interrupt device is configured so as to be capable of preventing further overcharge by interrupting a charging path of the battery based on the generation of gas.
When using the current interrupt device described above, a method is known in which a compound with a lower oxidation potential than an electrolyte (in other words, a compound with a lower start voltage of an oxidation decomposition reaction than the electrolyte: hereinafter sometimes referred to as an “overcharge inhibitor”) is included in the electrolyte in advance. Once the battery enters an overcharged state, the overcharge inhibitor is rapidly oxidized and decomposed on a surface of a positive electrode and hydrogen ions (H+) are created. As the hydrogen ions spread through the electrolyte and are reduced upon reaching a negative electrode, hydrogen gas is generated. Since pressure inside the battery case rises due to the generated hydrogen gas, the current interrupt device can be actuated more rapidly. For example, Patent Literature 1 discloses that cyclohexylbenzene (CHB) and biphenyl (BP) can be used as the overcharge inhibitor.